Experimental Investigation and Thermodynamic Optimization of the Na2O-FeO-Fe2O3-Al2O3-SiO2 System

English Abstract:

The Na₂O-FeO-Fe₂O₃-Al₂O₃-SiO₂ system possesses many minerals of importance for geology and metallurgy such as wüstite, spinel, corundum, aegirine, nepheline (carnegieite), albite, jadeite, fayalite, and silica (quartz, tridymite, cristobalite). Phase equilibria among these minerals and other compounds of this system are indeed very complex due to the change in Fe oxidation state with oxygen partial pressure and the substitution of Fe by Al. In the present study, a coupled experimental study and thermodynamic modeling approach was used to optimize the phase diagrams and thermodynamic properties of the whole system at 1 atm. New experiments were carried out in the Na₂O-FeO-Fe₂O₃-Al₂O₃ system in air and at Fe saturation, a critical evaluation of all experimental phase diagrams and thermodynamic property data available in the literature was performed, and new thermodynamic models were developed to create a new thermodynamic database that describes the Na₂O-FeO-Fe₂O₃-Al₂O₃-SiO₂ system. All the data were reproduced within experimental error limits from 298 K to above liquidus temperatures for all compositions and oxygen partial pressures from metallic Fe saturation to air. The phase equilibria and thermodynamic properties of this multi-component system at 1 atm were reasonably predicted using only binary and ternary model parameters.